If you need to pass multiple arrays to a subroutine, you need to use array references - see perlref, perlretut, perllol and/or perldsc. It might look something like:

#!/usr/bin/perl
use strict;
use warnings;

my @arrays = (
    [1,2,3],
    [6,32,6,87],
    [2,456,56,7,3324,6,4365],
);

iterator(@arrays);

sub iterator
{
    for my $array_ref (@_) {
        my $avg  = average(@$array_ref);
        print "Your average is $avg\n"
    }
    
}

sub average
      {
      my @stuff = @_;
      my $sum = 0;
      ($sum+=$_) for @stuff;
      my $average = $sum / @_;
      return $average;
      }
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